KR102232134B1 - Casting methods and curable compounds for electronic components or groups of parts - Google Patents

Abstract

The present invention relates to a method for casting an electronic component, wherein the component (1) is embedded in a casting compound (4), and then the casting compound (4) is cured through at least one crosslinking process. Further, the present invention relates to a curable compound that can be used as the casting compound (4) in the above method. The casting compound (4) contains at least one crosslinking component, the crosslinking component being uniformly distributed in the casting compound (4) and crosslinking to form at least two different crosslinking systems. Of the above crosslinking systems, the first crosslinking system 8 has a higher crosslinking density than the second crosslinking system 7, and the crosslinking with the first crosslinking system 8 is different from the crosslinking with the second crosslinking system 7 Triggered through other events. When casting a part (1) or a group of parts, at least one crosslinking component of the casting compound (4) is cured in at least one first region (5) away from the part (1) to at least partially form a first crosslinking system. It forms (8) and is cured in a second region (6) directly surrounding at least part (1) to form a second crosslinking system (7). This method makes it possible to create a housing function for the electronic component 1 from the casting compound 4 while the interior of the casting compound 4 remains smooth.

Description

Casting methods and curable compounds for electronic components or groups of parts

The present invention relates to a method for casting an electronic component or group of parts, wherein a part or group of parts is embedded into a casting compound and then the casting compound is cured by at least one crosslinking process. In addition, the present invention relates to a curable compound that can be used as a casting compound for the method.

The casting of electronic components is an important component of the production of modern electronic systems. In order to select the right casting compound, it must be determined whether a softer casting compound or a harder casting compound should be used for casting the part.

Soft casting compounds can compensate for stresses arising from, for example, shrinkage during curing or due to very different coefficients of thermal expansion during temperature changes. However, soft casting compounds often do not provide sufficient protection against external mechanical or chemical loads. The protection of the components against these loads must be achieved by a separate housing. Rigid casting compounds provide good protection for electronic devices from chemicals and mechanical loads, but are less suitable for stress reduction than softer materials. In cast electronic components, mechanical stresses are formed due to temperature fluctuations, usually due to very different coefficients of thermal expansion of the part and the casting compound, which can damage the electrical component when using a hard casting compound. In addition, the reaction shrinkage of hard casting compounds is usually more severe. This can, in the worst case, cause separation of the electronic component from the circuit board.

In the electronics field, casting compounds must perform several functions. The casting compound must completely enclose the electronic component to prevent the penetration of moisture, dust, foreign matter, water, chemicals, etc., and in particular, must provide effective corrosion protection for electronic components. In addition, the cladding must ensure electrical insulation of electronic components to increase withstand voltage and contact protection. The casting compound should fix the parts together and increase the mechanical stability and vibration resistance and impact resistance of the cast electronic component. In addition, the cavity must be filled with the casting compound and the heat dissipation from the electronic component must be improved.

Casting compounds known in the electronics industry are primarily reactive resin formulations. There are generally one-component and two-component systems with good flowability (low viscosity) to enclose the part to be cast without bubbles. Commercially available casting compounds are based on, for example, polyurethanes, acrylates, unsaturated polyester resins, epoxy resins or silicones. Typically these resin systems are cured through radical mechanisms or multiple additions. Due to this, there is an unclear variety of different types on the market that are optimized for each purpose of use. All casting compounds known to date give rise to uniformly crosslinked castings with uniform properties such as stiffness, shrinkage, expansion behavior, etc., regardless of the reactive resins or fillers used. In addition to the cold cure type and heat cure type, there are also UV cure casting compounds with very short curing times.

However, when casting electronic components or groups of parts from known casting compounds, a compromise must be made between the above advantages and disadvantages of a harder casting compound and a softer casting compound. In this case, the problem is that the rigid and rigid casting compound, which is rigidly crosslinked, on the one hand provides good mechanical protection and has high chemical resistance, while the crosslinking system of the narrow mesh on the other hand is associated with high processing shrinkage. Is that it induces high mechanical residual stress along with high stiffness. This leads to undesired high stresses of sensitive and detailed electronic components. In particular, the use of rigid casting mixtures is not allowed because the microstructured contacts on the circuit board are prone to breakage by stress. As an alternative to this, a partially elastomeric type, soft casting compound can be used, which has less shrinkage and lower stiffness, thus keeping the stress arising on curing or temperature fluctuating loads small. However, they often do not provide satisfactory mechanical protection and can be swollen and penetrated by chemical media. In a few exceptions, a number of different casting compounds are used in combination and laminated and cast, but this increases the production risk and in particular the cost for quality assurance.

Soft and hard casting compounds are generally used when casting electronic components or groups of parts, and additionally a separate metal or plastic housing surrounds the cast electronic device. The housing is often used as a kind of mold that is simultaneously cast into a casting compound. In this way, the electronic device can be protected from mechanical vibrations, for example by a soft curable casting compound, and the sealed housing protects the entire part from external mechanical influences or chemical attack. However, this increases the manufacturing cost and requires a much larger installation space than the electronic component itself.

An object of the present invention is to provide a casting method and a curable compound for an electronic component or group of parts substantially avoiding the above disadvantages when using a soft or hard casting compound. The method should allow casting without an outer housing for a cast part or a group of cast parts.

This problem is solved by the casting method and the curable compound according to claims 1 and 8. Preferred embodiments of the above casting method and curable compound are the subject of the dependent claims or appear in the following description and examples.

In the proposed method for casting an electronic component or group of parts, the part or group of parts is embedded in a casting compound, and then the casting compound is cured through at least one crosslinking process. In the above method, a casting compound having a crosslinking component A is used for casting, and the crosslinking component A is uniformly distributed in the casting compound, and can be crosslinked to form at least two different crosslinking systems, and the first of the crosslinking systems One crosslinking system is characterized by having a higher crosslinking density than the second crosslinking system. Crosslinking to the first crosslinking system is triggered through an event different from crosslinking to the second crosslinking system. In the proposed method, at least one crosslinking component A of the casting compound is cured in at least one first region away from the electronic component or group of electronic components to at least partially form a first crosslinking system, and at least the electronic component or electronic component It is cured in a second region directly surrounding the group to form a second crosslinking system.

Thus, the method enables the casting of parts without problems arising when using soft or hard casting compounds. In the region of contact with the part or group of parts, a soft region of the casting compound is formed by the lower crosslinking density, by which the mechanical stress due for example different thermal conduction behavior or reaction shrinkage of the casting compound is It can be avoided. This results in a less mechanical load, resulting in a more reliable part or group of parts. At the same time, a higher stiffness is achieved in the first region with a higher crosslinking density, and by this higher stiffness, a corresponding protective function can be exerted for the cast part or group of cast parts. Since the first region can perform the function of the housing, in a preferred embodiment of the method, a previously required working step of the additional housing can be saved by a corresponding crosslinking step of the casting compound in the first region. By the omission of the outer housing made possible accordingly, the cast electronic component or the entire component with the cast electronic component group can be formed more compactly, and thus an increase in the integration density can be achieved. The proposed method makes it possible to create a housing function from the casting compound while the interior of the casting compound remains smooth. Thus, there is no need to make a compromise by choosing a softer or harder casting compound. The method still uses a single casting compound that can be cured by a combination of different curing mechanisms to form different crosslinking systems and thus regions of different stiffness locally.

Preferably, in this case, a casting compound in which the first crosslinking system is formed only of at least one crosslinking component A is used, the casting compound comprises at least one second component, and the second component is homogeneously distributed in the casting compound. And the at least one crosslinking component A together with the second component forms a second crosslinking system.

The crosslinking component A and the second component B of the casting compound are preferably selected so that the two crosslinking systems different in modulus of elasticity differ by at least a factor 2. Preferably, the modulus of elasticity of the hard or rigid region is 300 to 3000 MPa, more preferably 500 to 2000 MPa. The elastic modulus of the soft region is preferably 0.5 to 200 MPa, more preferably 1 to 100 MPa.

A locally limited curing of at least one crosslinking component A of the casting compound in the first region is preferably carried out completely, so that the non-crosslinking component of the crosslinking component A does not remain in this region. However, this is not necessary. Surprisingly, in the case of partial curing or crosslinking with the first crosslinking system, it has been shown that the component that is still not crosslinked reacts with component B in this area by the trigger of the second event to form a second crosslinking system. That is, by incomplete crosslinking of component A, a region having a crosslinking density lying between the crosslinking density of the first crosslinking system and the crosslinking density of the second crosslinking system can be formed. In this area, the modulus of elasticity lies between that of the first crosslinking system and that of the second crosslinking system.

In the case of complete or partial crosslinking of at least one crosslinking component A in the first region, no component A remains or only a reduced amount of component A remains, and component B together with component A can form a second crosslinking system. have. Due to this, component B in this region remains unreacted in the first crosslinking system after triggering of the second event. Surprisingly, by adding component C, which does not react with component A and reacts with component B, in regions where component A is absent or only present in shortfalls, excess component B can be bound by formation of an additional crosslinking system. Turned out to be. In addition, component C can react with the binders involved in the reaction of component A and component B, so whether the formation of a crosslinking system of component A triggered by the first event in one region has been completely, partially or not at all. Regardless of whether or not this was not done, no unreacted components remain in the cured compound after the second event in all areas.

Casting of parts or groups of parts can be carried out in a variety of ways. In one embodiment, the electronic component or group of electronic components to be cast is introduced into the upwardly open housing, and then the casting compound is filled into the housing to cast the electronic component or group of electronic components into the casting compound. Then, at least one crosslinking component A of the casting compound is cured in the lower region surrounding the part or group of parts (second region) to form a second crosslinking system and the region containing the upper interface of the cast compound (first Area) at least partially curing to form the first crosslinking system. The casting compound in the lower region has a lower crosslinking density, and the upper closed region with a higher crosslinking density is formed more rigidly and thus can be used as a closure of the housing.

In another embodiment, the entire part or group of parts is cured in the (first) region surrounding the second region of the casting compound to form a first crosslinking system and thus comprises a softer (second) region of the casting compound. It completely surrounds the component that is being used. As a result, a housingless casting becomes possible since the outer, more rigid area (first area) of the casting compound can fully perform the function of the housing in this case. This measure can be preferably carried out in such a way that the casting compound is molded and cured during the casting of the electronic component or group of electronic components so that the appearance of the cured casting compound is brought close to the contour of the electronic component or group of electronic components. This allows electronic components or groups of electronic components to be cast into very compact components. Casting can be carried out by means of a mold or without tools, respectively.

A preferred possibility of tool-free casting of parts or groups of parts with the casting compound is to apply the casting compound layer by layer by an additive manufacturing method and cure each layer by layer to form a first or second crosslinking system. Thus, in particular, the latter embodiment of housingless casting can be realized very simply.

The curing mechanism for crosslinking the components to be crosslinked to form the first and second crosslinking systems should be able to be triggered as simple and inexpensively as possible. Preferably the component A to be crosslinked and optionally one or more additives in the casting compound are selected such that the crosslinking component A is crosslinked by radiation curing, such as UV radiation curing, to form a first crosslinking system. This crosslinking can be performed simply and inexpensively. For crosslinking to the second crosslinking system, component A to be crosslinked and optionally one or more additives in the casting compound are preferably selected so that crosslinking to the second crosslinking system can be carried out by a thermal curing technique. By this combination of radiation curing and thermal curing, at least one crosslinking component A of the casting compound is first cured in at least one first region to form a first crosslinking system, and then cured in the remaining regions to form a second crosslinking system. A variant of the method of forming can be carried out particularly simply. Of course, there may also be other curing mechanisms that allow for this measure. In the case of radiation curing, optical radiation in the wavelength range of 100 nm to 700 nm, more preferably in the wavelength range of 250 nm to 450 nm is preferably used. The heat treatment for thermal curing is preferably performed at a temperature in the range of 60°C to 300°C, more preferably 110°C to 180°C. In a preferred embodiment, the temperature during curing is increased continuously or stepwise upon thermal curing.

Implementation of the proposed method requires the use of properly formulated casting compounds with adjustable and locally controllable stiffness. To this end, the casting compound must contain at least one crosslinking component A which is cured by two different curing mechanisms to form two different densities of crosslinking systems. Given the above conditions, a person skilled in the art will be able to prepare a suitable casting compound having the predetermined properties.

The curable compound proposed according to the invention that can be used in the above-described method comprises at least one crosslinking component A, wherein the crosslinking component A is uniformly distributed in the curable compound and can be crosslinked to form at least two different crosslinking systems. Wherein the first crosslinking system of the crosslinking systems is formed of only at least one crosslinking component A, and at least partial crosslinking of the curable compound from at least one first region (i) to the first crosslinking system is a first event Can be triggered through. The curable compound also comprises at least one second component B, wherein the second component B is uniformly distributed in the curable compound and forms a second crosslinking system of at least two different crosslinking systems with at least one crosslinking component A. And the second crosslinking system has a lower crosslinking density than the first crosslinking system. Crosslinking to the second crosslinking system may be triggered via a second event in at least one second region (ii) of the curable compound, in which the first crosslinking system is not formed or only partially formed. The curable compound also comprises at least one third component C, wherein the third component C is uniformly distributed in the curable compound and after at least partial crosslinking with the first crosslinking system, the first region (i) and the second region ( In ii) at least one second component B reacts with the uncrosslinked component to form a further crosslinking system. The reaction of the third component C and the second component B is triggered by a second event.

In a preferred embodiment, the third component C reacts with a crosslinking point resulting from the reaction of at least one component A with at least one component B in at least one second region (ii) in which the first event is not triggered, thereby further It is chosen to be able to form a crosslinking system.

Preferably, the crosslinking component A, the second component B and the third component C are selected such that the modulus of elasticity of the first region (i) and the second region (ii) differ after curing by at least a factor 2.

Said at least one crosslinking component A is preferably a compound having at least two functional groups, in particular double bonds. Particularly preferred are compounds having at least two acrylate groups. Examples of such components are esters of acrylic acid or methacrylic acid of higher alcohols, such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetra and polyethylene glycol. Di(meth)acrylate, 1,3-butanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonane Diol dimethacrylate, glycerol di(meth)acrylate, diurethane dimethacrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, 2,2- Bis(4-methacryloxyphenyl) propane, 1,10-decanediol dimethacrylate, 1,5-pentanediol dimethacrylate, 1,4-phenylenediacrylate, tricyclodecanedimethanol dimethacryl Rate (available as SR833 from Sartomer/Arkema), tris(2-hydroxyethyl)-isocyanurate triacrylate (available as SR368 from Sartomer/Arkema, for example). Preferably, the curable compound comprises at least one additional component D, and the additional component D generates a radical capable of crosslinking at least one crosslinking component A by a radical chain reaction when irradiated with visible or UV light. do. One of skill in the art can find a number of such ingredients, also called photoinitiators, that meet these conditions, for example in BASF's product catalog under the trade name Irgacure. Examples of the component D forming radicals by irradiation are bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 1-hydroxy-cyclohexyl-phenyl-ketone, 2-hydroxy-2-methyl -1-phenyl-1-propanone, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methylpropane-1- on, 2-hydroxy-1-[4-(2-hydroxy ethoxy)phenyl]-2-methyl-1-propanone, 2,4,6-trimethylbenzoyl diphenylphosphinate, 2,4, 6-trimethylbenzoyl diphenylphosphine oxide, 2-methyl-1[4-(methylthio)phenyl]-2-morpholinopropane-1-on, 2-benzyl-2-dimethylamino-1-(4- Morpholinophenyl)-butanone-1, 2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-on or benzophenone .

The at least one second component B is preferably a compound having at least two functional groups, in particular a compound having at least two groups which can be added by Michael addition reaction, for example in a double bond. These are in particular amine groups, thiol groups or phosphine groups. It is particularly preferred to use compounds having at least two amine groups. At least the second component B is preferably the following general formula

R-(NH ₂ ) _n

It is selected from compounds having, wherein R may be a hydrocarbon or other organic monomer, oligomer or polymer compound containing a hetero atom, and may be a linear or branched chain, or consist of one or more substituted or unsubstituted aliphatic or aromatic ring structures. It may be a group capable of, and at least two hydrogen atoms in the group are substituted with an amine group. Examples of these are ethylenediamine, diethylenetriamine, triethylenetetraamine, isophoronediamine, 1,6-hexanediamine, toluenediamine, 4,4'-diphenylmethanediamine, 2,4'-diphenylmethanediamine , 1,3-diaminopentane, 2,2,4-trimethylhexane-1, 6-diamine, 1,4-diaminobutane, polyethylene glycol diamine, polypropylene glycol diamine, or commercial product Jeffamine D-400 from Huntsman Or Jeffamine D-2000 or Croda's hardener Priamine 1071, Priamine 1073, Priamine 1074 or Priamine 1075.

Preferably, the curable compound comprises at least one further component E which catalyzes the reaction between at least one crosslinking component A and at least one second component B. Preferably non-nucleophilic bases such as tertiary amines are used. Examples for the additional component E are 1,8-diazabicyclo[5.4.0]undec-7-en (DBU), 1,5-diazabicyclo[4.3.0]non-5-en (DBN), Triethylenediamine (DABCO), 4-(dimethylamino)pyridine (DMAP), N,N-diisopropylethylamine (DIPEA) or 2,6-Di-tert-butyl pyridine.

At least one third component C is preferably a compound having at least two functional groups, in particular epoxide functional groups. Examples for component C include bisphenol-A-diglycidyl ether (DGEBA), and its oligomers sold under the trade name Epilox A in various variations, such as from the company Leuna-Harze, bisphenol-F-diglycidyl ether, and For example, its oligomer sold under the trade name Epilox F from Leuna-Harz, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, 1,3-bis (2,3-epoxypropoxy)-2,2-dimethylpropane, 1,2-epoxy-3-(2-methylphenoxy)propane, 1,4-bis(2,3-epoxypropyloxy)butane, Cyclohexanedimethanol diglycidyl ether, glycerol triclisityl ether, neopentyl glycol diglycidyl ether, pentaerythritol polyglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether Or epoxidized vegetable fat.

In a preferred embodiment, the mixing ratio between components A, B and C is the crosslinking systems in which 99% or more of components A, B and C are formed after the occurrence of the first and second events in at least one first region (i). Included in at least one of the crosslinking systems, 1% or less of the functional groups of components A, B and C remain, and components A, B and C after the occurrence of the second event alone in at least one second region (ii) It is selected so that at least 99% of is included into the second crosslinking system, and less than 1% of the functional groups of components A, B and C remain.

The curable compound may also comprise at least one filler or reinforcing material in a proportion of 1 to 99% by weight, preferably 20 to 80% by weight, more preferably 40 to 70% by weight.

The curing of the proposed curable compound is preferably triggered by a first event forming a first crosslinking system in at least a portion of the compound having a higher crosslinking density than at least one other region, and a second crosslinking over the entire volume of the compound. A second event forming the system is made to be triggered.

Examples of curable compounds suitable for use in the proposed method are described below.

With the proposed method and the proposed curable compound, the advantages of the two variants are integrated, thereby avoiding the dilemma of the choice between hard and soft casting compounds in the field of electronic devices. By the above method, it is also possible to realize housingless casting of electronic systems, such as semiconductor modules, sensors, control electronics, power electronics, etc., with a variable hardening casting compound, because the hard outer layer performs the function of the housing. Because. This can be done completely without tools in additive manufacturing processes such as stereolithography, for example. Electronic components can equally be used in many fields, such as the automotive industry, white goods or consumer electronics.

The proposed method and the proposed curable compound will be described in detail below with reference to examples together with the drawings.
1 shows an embodiment of a part cast according to the prior art,
2 shows an embodiment of a part cast according to the present method,
3 shows another embodiment of a part cast according to the present method,
4 shows another embodiment of a part cast according to the present method,
5 is a schematic diagram of crosslinking systems of different densities used in the present method,
6 is a schematic diagram of base catalyzed Aza-Michael addition of amine to acrylate,
7 is a tensile/strain diagram of the specimen of the first embodiment,
8 is a diagram showing a curve of Shore hardness A according to the depth of the specimen,
9 is a tensile/strain diagram of the specimen of the second embodiment,
10 is a tensile/strain diagram of the specimen according to the third embodiment.

The following figures show various possibilities for casting electronic components from casting compounds. 1 shows a conventional method according to the prior art, in which the electronic component 1 is inserted into the housing 3 on the circuit board 2, and then a relatively soft curable casting compound in the housing 3 It is cast as (4). After that, the housing 3 is completely closed with the housing cover.

In the method according to the invention, casting compounds are used which can be cured according to the curing mechanism used for curing, for example radiation curing or thermal curing, to form crosslinking systems of different stiffness or density. This allows the setting of locally different stiffness of the casting compound through the selection and topical application of the respective curing mechanism. In the proposed method, the electronic component can be surrounded by a soft core material of a casting compound, which core material simultaneously forms a rigid outer layer. In this way, since the stress in the core region can be relieved, damage to the electronic device can be prevented. At the same time, by means of a rigid outer layer of the cured casting compound, the housing function or at least part of the housing function can be realized.

For example, FIG. 2 shows an embodiment according to the present invention in which the electronic component 1 on the circuit board 2 is first inserted into the upwardly open housing 3. The casting compound 4 is then filled into the housing and cured by a first curing mechanism in the upper first region 5 to form a higher density first crosslinking system. In a second region 6 directly surrounding the electrical component 1, the casting compound 4 is cured by a second curing mechanism, forming a second crosslinking system with a lower crosslinking density. Due to the higher crosslinking density in the upper region 5, the cast compound cured in this region is much more rigid than in the inner core region, i.e. the second region 6 with a second crosslinking system, so that the first region ( The function of the housing cover can be performed by 5). As in the embodiment of Figure 1, there is no need for an additional part for closing the housing.

In the proposed method, a separate housing as schematically shown in the embodiment of FIG. 3 may be completely omitted. Here, the electronic component 1 on the circuit board 2 is completely surrounded by the second (softer) region 6 of the cast compound 4. The second area 6 is completely surrounded by the first (more rigid) area 5 of the casting compound 4. The first region 5 here serves as a housing to protect the electronic component 1 from penetration of moisture, dust, foreign matter, water, chemicals, and the like. This configuration can be formed by casting into a suitable mold, after which the mold is removed. Another possibility is to use an additive manufacturing method in which a casting compound 4 is applied layer by layer and cured to completely surround the electronic component 1 on the circuit board 2. This enables tool-free and housing-free casting of electronic components. In this additive manufacturing method, curing takes place layer by layer, ie after each application of each layer.

Using this additive manufacturing technique, casting close to the contour of the electronic component 1 on the circuit board 2 is possible, as schematically shown in FIG. 4. Thus, with the proposed method and the gradient casting compound used therein, toolless, housingless and near-contour casting of electronic components or groups of parts is possible.

In the proposed method, the curable compound is used as a casting compound, which can be cured by different curing mechanisms to form crosslinking systems of different stiffness. For the development or provision of such compounds, one skilled in the art can use a variety of possibilities and combinations of materials. In the following example, a curable compound is prepared in which the curing mechanism (second curing mechanism) acts over the entire volume of the compound to create a wide mesh crosslinking system with a low crosslink density. The resulting material is soft to rubbery elastic. An additional curing or crosslinking mechanism (first curing mechanism) acts locally, for example only on the surface, and produces a high crosslinking density, which results in a more rigid material. This is schematically illustrated in FIG. 5. In the upper partial figure, a crosslinking system 7 with a low crosslinking density is shown, which can be produced by a second curing mechanism, which spans the entire volume and produces an elastomeric material. In the lower partial drawing, a region 8 with a locally higher crosslinking density is shown inside the crosslinking system 7 of the upper partial drawing, the higher crosslinking density obtained by a locally acting first curing mechanism. Makes high and rigid materials. The crosslinking component A and the two curing mechanisms of the curable compound are selected such that the second curing mechanism acts over the entire volume of the curable compound, while the first curing mechanism acts only locally. By the combination of the two curing mechanisms, the crosslinking density of the curable compound and its stiffness can be controlled as intended.

It is important to note in the preparation of these compounds that both mechanisms result in a stable final state. After curing, in the soft region and the rigid region, there may not be a large amount of reactive groups remaining that can cause post-crosslinking of the compound. Complete curing of all components is a prerequisite for long-term stability at varying temperatures. The functional groups required to increase the crosslinking density must react locally, for example in the first curing step and enter into the wide mesh crosslinking system in the second curing step. However, an increase in crosslinking density or stiffness cannot be achieved. Thus, at least one material used as crosslinking component A must be capable of forming a crosslinking system in two different ways.

Examples of suitable base materials for such curable compounds are the class of acrylates as crosslinking component A with various possibilities of forming crosslinking systems. The simplest method is radical polymerization, which can be initiated either by heat or by ultraviolet rays in the presence of a radical generator. Acrylates can also be polymerized anionic or cationic. Another mechanism for curing the acrylate is the Michael addition reaction. This allows for the base catalyzed addition of the amine to the CC double bond of the acrylate, for example as shown in Figure 6. This variant has an advantage over the proposed method, since, unlike in the case of radical polymerization, the acrylate is not directly linked to other acrylate groups but via an amine curing agent as the second component B. This means that in this type of polymerization the crosslinking density can be controlled by the type of amine curing agent and thus is significantly different from the crosslinking density of radical polymerization. When a long chain, flexible amine curing agent is used with an acrylate to form a high rigid material having a high T _g (T _{g: glass transition temperature) as a homopolymer, a soft material having elastomeric properties can be produced.} Thus, the reaction of Michael addition of amines to acrylates is a preferred mechanism for meeting the conditions described above. However, the proposed method is not limited to acrylate or the above mechanism, and those skilled in the art will always be able to find other basic materials and mechanisms that meet the conditions of the proposed method.

In this embodiment, radical polymerization of acrylates is selected as a mechanism capable of locally triggering the formation of a rigid material. It is not activated by heat, but by UV irradiation with a suitable photo initiator. In particular, in the application provided herein of casting compounds for housingless casting of electronic components, this variant offers clear advantages. Radiation curing enables the intended triggering of radical acrylate polymerization in the outer region of the curable compound, and thus the creation of a rigid sheath that can later function as a housing. At the same time, the depth of penetration of the UV radiation and thus the thickness of the hard outer layer can be controlled, not only by the radiation intensity or the duration of the radiation, but also by the type of photoinitiator or by the filler.

Thus, in order to combine the radical polymerization of acrylates and Michael addition of amines to the acrylates in the formulation of curable compounds with adjustable mechanical properties, an acrylate resin (component A) having very high stiffness and strength as a homopolymer, and A suitable photoinitiator (component D) is required. On the other hand, in the case of Michael addition, a flexible amine curing agent (component B) and a non-nucleophilic strong base (component E) as catalyst are required to produce a material with elastomeric properties in this way. In the irradiated area, the acrylate reacts with itself, and in the non-irradiated area, it reacts with the amine curing agent. Thus, the acrylate is completely consumed in the soft and rigid areas and can no longer be post-crosslinked. After the rigid material is formed by UV treatment, the unreacted amine curing agent remains in the crosslinking system. They are not as dangerous as possible with respect to the post-bridge. However, in a preferred embodiment, they can also be combined in a crosslinking system to avoid washing of the components and consequently changing the material properties over time. This can be done, for example, via an epoxy resin as an additional component C.

The number of commercially available multifunctional acrylates is large, including, for example, products SR834, SR833S and SR368 from Sartomer/Arkema and some types of VISIOMER series from Evonik. The choice of amine curing agent is very wide and includes many compounds. Examples include hardeners DETA, TETA, 2,2,4-trimethylhexane-1,6-diamine, 1,4-diaminobutane from Sigma-Aldrich or IDPA, hardener Jeffamine D-400 or Jeffamine D-2000 from Huntsman, or Croda's hardeners include Priamine 1071, Priamine 1073, Priamine 1074 or Priamine 1075.

As described above, if the second resin component must be used to bond the unreacted amine curing agent in the crosslinking system, various epoxides from Leuna-Harze and Ipox-Chemicals are provided that can react with the residual amine after irradiation. . For this, for example, products Epilox P 13-20 from Leuna-Harze, Epilox P 13-26, Epilox P 13-42, Epilox P 13-30 or IPOX ER 15 from DGEBA and Ipox-Chemicals may be used. Photoinitiators, accelerators and catalysts include, for example, Irgacure 184 or Irgacure 819 from BASF, which is a photo initiator for radical polymerization of acrylates, Accelerator 960-1 from Huntsman, which is an accelerator for curing amine epoxy, and non-nucleophilic as a catalyst for Michael addition The bases of Sigma-Aldrich's diazabicyclononene (DBN), diazabicyclodecene (DBU), triazabicyclodecene (TBD), triethylenediamine (DABCO) can be used.

The main component of the formulation of the casting compound or curable compound selected in this example is an acrylate, preferably SR833S, SR368, and a mixture of both. As the proportion of foreign substances or additives (amine, epoxide, initiator, base catalyst) increases, UV curing becomes increasingly difficult, which may reduce stiffness or strength in the exposed area. A proportion of 0.5 to 0.65 g of foreign matter per 1 g of acrylate appears to be particularly preferred. The foreign material consists of a large amount of different amines, a small amount of epoxide and a very small amount of initiator/catalyst/accelerator. To obtain the desired curable compound, the foreign substances were combined and then mixed with Hauschild's Speedmixer™ DAC400.1 VAC-P (1:30 min, 2500 rpm, 20 mbar).

For testing, specimens for tensile testing were made of curable compounds. To this end, the curable compound was filled into a silicone mold in the form of a tensile rod. To obtain a soft material, unexposed samples were stored at different curing temperatures. To obtain a rigid material, the sample was first irradiated in a UV irradiation chamber (UVA-CUBE 2000, Hoehnle, 2000W, 15 cm distance from the tube) and then stored in an oven. The curing temperature and curing duration are shown in the examples below. To clarify the difference in mechanical and thermal properties, samples prepared in this manner were tensile tested, tested for Shore hardness A, and measured at glass temperature using DSC (differential scanning calorimetry) and DMA (dynamic mechanical analysis). Was inspected. Three examples of a large number of test series are presented below.

Example 1:

In the first embodiment, SR368 is used as an acrylate component. Amino terminal polyethers of different chain lengths (Jeffamine D-400 and D-2000) and IPDA are used as the amine component. As an epoxy resin, the formulation is mixed with an alicyclic IPOX ER 15 to bind the amine curing agent. DBU is used to catalyze the Michael addition reaction. Irgacure 819 is used as a photoinitiator for the manufacture of 2 mm thick tensile specimens, and Irgacure 184 is used for testing the penetration depth of radiation. The formulation of the curable compound thus prepared has the composition shown in the table below.

ingredient amount SR368 5g IPOX ER 15 0.5g Jeffamine D-2000 1g Jeffamine D-400 0.7g IPDA 0.85g Irgacure 184 or 819 10mg DBU 50mg

After filling the specimen mold, half of the sample was irradiated for 2 minutes in UVA-CUBE 2000, while the other half was protected from light irradiation. All samples were then cured together in an oven at 110° C. for 2 hours and 180° C. for 1 hour. After irradiation, the previously transparent specimen becomes opaque, indicating a phase separation between the polymerized acrylate and the epoxide or amine curing agent. This is preferred because the polymerized acrylate phase must maintain the physical and mechanical properties of the homopolymer, i.e. high glass transition temperature T _g and high stiffness. Samples cured only by heat remain transparent. That is, a uniform crosslinking system is formed. A rigid, hard material was formed in the exposed area, and a soft rubber elastic material was formed in the unexposed area. The measurement results of the tensile sample are shown in the tensile-strain diagram of FIG. 7 and the table below.

Psalter Tensile test Shore hardness A DSC DMA Modulus of elasticity
[MPa] σ _B
[MPa] ε _B
[%] T _g
[°C] T _g
[°C] Stiffness 850.1 41.7 7.6 46 - 132.1 Soft 21.3 3.6 130.7 76 10.7 -

The figure clearly shows the high stiffness of the specimen by UV and thermal curing, and the purely thermally cured specimen has high elasticity. Purely heat cured compounds have very low stiffness and high ductility, similar to elastomers. However, when the compound is irradiated, the stiffness increases enormously at the expense of ductility. Conditions for a stable gradient are also met by this exemplary formulation. To this end, the specimens were examined for secondary reactions by DSC. There was no secondary reaction in the temperature range of -75°C to 200°C in the soft or rigid samples. Thus, since reactive groups are completely consumed in the two types of samples, permanent stiffness differences can be created by irradiation.

To test whether this type of formulation is suitable for housingless casting of electronic components, the photoinitiator Irgacure 819 has been replaced by Irgacure 184. Irgacure 819 is suitable for curing thicker layers because it decomposes by irradiation with wavelengths in the visible range of the spectrum. In contrast, Irgacure 184 has an absorption maximum at a wavelength of about 250 nm. In other words, the absorption of the used resin system appears accurately within the expected range. This is to ensure that the depth of penetration of the radiation in the relevant wavelength range is kept as low as possible in order to create a thin rigid edge layer that can later function as a housing. To investigate the effect of the duration of irradiation on the penetration depth of UV radiation when using Irgacure 184, a polystyrene cuvette was wrapped with black insulating tape and 3 g of the above formulation was filled. The samples were then exposed to different lengths of UV radiation and then thermally cured according to the above heating program. 8 shows curves of surface hardness with sample depth at different irradiation durations.

As can be seen from FIG. 8, the penetration depth of the UV radiation increases with an increase in the irradiation duration. At a duration of about 60 seconds, a saturation value of about 4 mm penetration depth is achieved. When transitioning from the rigid region to the soft region, the surface hardness of the sample decreases. After a few millimeters below the rigid layer, the shore hardness is 30-40% lower than that of the rigid area. This test shows that the layer thickness of the outer rigid layer, which will later function as a housing, can be controlled as intended by the type of photoinitiator and the duration of irradiation.

Example 2:

In Example 2, SR368 and SR833S were used as acrylate components. Polyethers of different chain lengths (Jeffamine D-400 and D-2000) and IPDA are used as the amine component. As an epoxy resin, the formulation DGEBA is mixed to bind the amine curing agent. DBU is used to catalyze the Michael addition reaction. As a photoinitiator, Irgacure 819 is used. From these components, the following formulations of curable compounds are produced:

ingredient amount SR368 1 g SR833S 4 g DGEBA 0.5 g Jeffamine D-2000 1 g Jeffamine D-400 0.7 g IPDA 0.85 g Irgacure 819 10 mg DBU 50 mg

After filling the specimen mold, half of the sample was irradiated for 5 minutes in UVA-CUBE 2000, while the other half was protected from light irradiation. All samples were then cured together in an oven at 110° C. for 2 hours and 180° C. for 2 hours. Here, in the exposed area, a rigid transparent specimen was obtained, and as a result, no phase separation occurred. Acrylate SR833S resulted in better mixing and integration of unreacted components after irradiation. Transparency here is not an indication of lower stiffness, which is evidenced by the measurement results shown in Fig. 9 and the table below. 9 again shows the measurement results of the tensile sample in the tensile-strain diagram.

Psalter Tensile test Shore hardness A DSC DMA Modulus of elasticity [MPa] σ _B
[MPa] ε _B
[%] T _g
[°C] T _g
[°C] Stiffness 606.7 26.8 7.2 10 - 116.5 Soft 0.7 0.5 144.1 70 -5.4 -

This formulation provides a softer material than Example 1 in the unexposed regions, as can be seen from the lower values for the glass transition temperature, Shore hardness A and modulus of elasticity. Exposed specimens show lower stiffness or strength after curing, but this is sufficient for housing function. The big advantage of the combination of SR368 and SR833S is that the viscosity decreases as the proportion of SR833S increases. Depending on the proportion of SR833S, the viscosity of the entire mixture can be adjusted, which can be advantageous for the use of fillers in terms of shrinkage and thermal conductivity. Using the second photoinitiator, Irgacure 184 to investigate the penetration depth, results very similar to Example 1 in this formulation, where the rigid and soft regions can no longer be visually distinguished. The stiffness of the exposed outer layer can be controlled by the type of initiator in this formulation and the duration of exposure. No secondary reaction was observed in the range of -75°C and 200°C. That is, curing is complete and all reactive groups are consumed.

Example 3:

In Example 3, SR833S was used as the acrylate component. Priamine (a mixture of aminated monomers of oleic acid, dimers and trimers; aliphatic backbone) and 2,2,4-trimethylhexane-1,6-diamine are used as amine components. As an epoxy resin, the formulation DGEBA is mixed to bind the amine curing agent. DBU is used to catalyze the Michael addition reaction. As a photoinitiator, Irgacure 819 is used. From these components, the following formulations of curable compounds are produced:

ingredient amount SR833S 5 g DGEBA 0.75 g Priamine 1075 0.74 g 2,2,4-trimethylhexane-1,6-diamine 1.26 g Irgacure 819 10 mg DBU 50 mg

After filling the specimen mold, half of the sample was irradiated for 5 minutes in UVA-CUBE 2000, while the other half was protected from light irradiation. All samples were then cured together in an oven at 110° C. for 2 hours and 150° C. for 2.5 hours and 180° C. for 1 hour. Here too, a transparent specimen is obtained. That is, excess amine/epoxide can be mixed with the acrylate crosslinking system and there is no phase separation. The measurement results of the tensile samples are presented in Fig. 10 and the table below.

Psalter Tensile test Shore hardness A DSC DMA Modulus of elasticity
[MPa] σ _B
[MPa] ε _B
[%] T _g
[°C] T _g
[°C] Stiffness 566 20.5 15.6 24 27.1 and 185.2 - Soft 4.2 2.9 138.6 74 12.1 -

Here too, a clear difference in stiffness is achieved, which makes it possible to use it as a casting compound in the proposed method. The advantage of the aliphatic backbone amines used here (Priamine and 2,2,4-trimethylhexane-1,6-diamine) is the higher temperature stability of the cured material. The soft and rigid parts of the casting compound retain their properties even after long-term storage at high temperatures, which is a clear advantage compared to Examples 1 and 2. Use at temperatures above 100° C. may be made possible with this formulation. Here too, no post-crosslinking was observed in the range of -50°C to 250°C, indicating a complete reaction of all components. The layer thickness of the rigid outer layer can also be controlled here by the duration of the exposure.

Many of the compounds proposed so far are not described in the examples presented, but can be used in the proposed method and in the corresponding formulation for the proposed curable compound. All of these compounds have a specific effect on curing and can be used for modification. For example, acrylate SR834 and base DBN and DABCO are used to slow the curing reaction compared to the examples described above, and other compounds are generally suitable for accelerating the reaction. With the use of some epoxides, the stiffness and strength of the two areas can be changed, which is also an important adjustment screw. All compounds have their own utility in the formulations developed and thus can be used according to the invention irrespective of the examples presented herein.

In summary, it may be mentioned that these formulations can be used as casting compounds or curable compounds having variable mechanical properties. By irradiating with UV light or visible light, the stiffness of the compound can be controlled as intended and can be produced particularly locally. At the same time, it is shown in Example 1 that the penetration depth of the relevant radiation (layer thickness in the rigid region) can be controlled by the type of photoinitiator and the irradiation intensity and irradiation duration. Thus, while a kind of housing function can be created by irradiation, the interior of the compound is smooth and the electronic device is enclosed without stress as much as possible. The application conditions are complete curing of all components of the curable compound, and the basic components are preferably locally crosslinked in time in a first curing step (e.g. UV; first curing mechanism), followed by a second curing step (e.g., to heat). By; in the second curing mechanism) it should enter into the wide mesh crosslinking system without increasing the stiffness. This condition can be met, for example, by a combination of light induced acrylate crosslinking and base catalyzed Michael addition. Of course, those skilled in the art will be able to readily find other mechanisms and/or components or formulations of curable compounds that meet the above conditions.

The formulations developed should preferably be selected so that the shrinkage and associated stresses produced during curing are minimal. In addition, electronic components generally generate heat that must be dissipated. At this point, the use of fillers may be desirable. In the field of electronics, generally electrically insulating, thermally conductive fillers are useful. These include, for example, quartz, aluminum compounds (oxides, hydroxides, boehmite, nitride), boron nitride and silicon carbide. A number of experiments using the above filler have shown significant shrinkage reduction and increase in thermal conductivity at filler content of 60% by weight or more. The maximum processing viscosity of the casting compound is 1000-10000 mPa*s, which can be achieved with the formulation proposed here even at high actual filling levels.

In the proposed method, from one and the same formulation of the curable compound, two materials that are completely different in terms of thermal and mechanical properties are prepared. Accordingly, a housing for an electronic component having a clear glass transition of the soft phase at low temperature can be realized, while a glass transition temperature of, for example, 110° C. or higher on the rigid phase is achieved. In terms of surface hardness and stiffness, considerably different properties are obtained. Thus, the method allows the casting of an electronic component or group of parts having a housing function from the casting compound while the interior of the casting compound is kept smooth. Such housing functions may be created by short irradiation steps in the second range in certain embodiments.

1 electronic components
2 circuit board
3 housing
4 casting compound
5 first area
6 second area
7 Crosslinking system with low crosslinking density
8 Crosslinking system with high crosslinking density

Claims (20)

An electronic component (1) or a group of parts is embedded into a casting compound (4), and the casting compound is cured through at least one crosslinking process, the method comprising:
-A casting compound (4) comprising at least one crosslinking component A is used, and the crosslinking component A is uniformly distributed in the casting compound (4), and can be crosslinked to form at least two different crosslinking systems, the Of the crosslinking systems, the first crosslinking system (8) is formed only of at least one crosslinking component A, and at least partial crosslinking with the first crosslinking system (8) is at least one first region of the cast compound (4). It can be triggered through the first event in (5),
-The casting compound (4) contains at least one second component B, the second component B is uniformly distributed in the casting compound (4), and the at least one crosslinking component A is the second component B Together with one of the at least two different crosslinking systems, the second crosslinking system 7 has a lower crosslinking density than the first crosslinking system 8, and the first crosslinking system 2 Crosslinking with the crosslinking system 7 is a second event in at least one second region 6 of the casting compound 4 in which the first crosslinking system 8 has not been formed or has been formed only partially. Can be triggered via
-Said casting compound (4) also comprises at least one third component C, said third component C being uniformly distributed in said casting compound (4), said at least in said first crosslinking system (8) After partial crosslinking reacts with the uncrosslinked portion of the at least one second component B in the first region 5 and the second region 6 to form an additional crosslinking system, and with the third component C The reaction of the second component B is triggered by the second event,
-The at least one crosslinking component A of the casting compound (4) is cured in at least one region away from the electronic component (1) or the electronic component group as a first region (5) to at least partially 1 forming a crosslinking system 8 and being cured in a region directly enclosing the electronic component 1 or the electronic component group as at least a second region 6 to form the second crosslinking system 7 A method of casting an electronic component or group of parts. The electronic component or component group according to claim 1, wherein the at least one crosslinking component A and the at least one second component B are selected such that two crosslinking systems having different modulus of elasticity are different by at least a factor 2. Casting method. 3. The electronic component (1) or the electronic component group to be cast is introduced into an upwardly open housing (3), and then the electronic component (1) or the electronic component group is transferred to the casting compound. For casting into (4), the casting compound (4) is filled into the housing (3), and the at least one crosslinking component A of the casting compound (4) comprises the upper interface of the casting compound (4). Which is cured at least partially in the region as the first region 5 to form the first crosslinking system 8, and at least in the remaining region as the second region 6 to form the second crosslinking system 7 A method for casting an electronic component or group of parts, characterized in that for forming. The crosslinking component A according to claim 1 or 2, wherein the crosslinking component A is cured in a layer of the casting compound (4) as a first region (5) to form the first crosslinking system (8), wherein the crosslinking component A is Forming an outer interface of the casting compound (4) and completely surrounding the second region (6) with the electronic component (1) or the group of electronic components. The electronic component (1) or the electronic component group according to claim 4, wherein the casting compound (4) is molded and cured at the time of casting of the electronic component (1) or the electronic component group, so that the appearance of the cured casting compound (4) is the electronic component (1) or An electronic component or component group casting method, characterized in that the electronic component or component group is brought close to a contour of the electronic component group. The electronic component or component according to claim 1 or 2, wherein the casting compound (4) is applied and cured layer by layer by an additive manufacturing method at the time of casting the electronic component (1) or the electronic component group. The group's casting method. As a curable compound that can be used as the casting compound (4) in the method according to claim 1 or 2, the curable compound is
-Contains at least one crosslinking component A, wherein the crosslinking component A is uniformly distributed in the curable compound, can be crosslinked to form at least two different crosslinking systems, the first of the crosslinking systems (8 ) Is formed only of the at least one crosslinking component A, and at least partial crosslinking of the curable compound from at least the first region (i) to the first crosslinking system 8 can be triggered through a first event,
-At least one second component B is included, wherein the second component B is uniformly distributed in the curable compound, and the at least one crosslinking component A is, together with the second component B, of the at least two different crosslinking systems. A second crosslinking system 7 can be formed, the second crosslinking system 7 has a lower crosslinking density than the first crosslinking system 8, and crosslinking with the second crosslinking system 7 , The first crosslinking system 8 may be triggered through a second event in at least one second region (ii) of the curable compound in which no or only partially formed,
-At least one third component C, wherein the third component C is uniformly distributed in the curable compound and after the at least partial crosslinking with the first crosslinking system 8 the first region (i) and In a second region (ii) reacts with the uncrosslinked portion of the at least one second component B to form an additional crosslinking system, and the reaction of the third component C with the second component B is the second event Triggered by, curable compounds. The method of claim 7, wherein the crosslinking component A, the second component B, and the third component C are selected so that the elastic modulus of the first region (i) and the second region (ii) differ by at least a factor 2. Curable compound made into. 8. The curable compound of claim 7, wherein the first event is treatment with visible light or UV-light. 8. The curable compound of claim 7, wherein the second event is a heat treatment. The curable compound according to claim 7, wherein the at least one crosslinking component A is a compound having at least two functional groups having a double bond. The method of claim 7, wherein the curable compound comprises at least one additional component D, and when the additional component D is irradiated with visible or UV-light, the at least one crosslinking component A is crosslinked by a radical chain reaction. Curable compound, characterized in that it generates radicals capable of. The method of claim 12, wherein the at least one component D forming a radical by irradiation is bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 1-hydroxy-cyclohexyl-phenyl-ketone or benzo. A curable compound characterized in that it is phenone. 8. The curable compound according to claim 7, wherein the at least one second component B is a compound having at least two functional groups having an amine group. The curable compound according to claim 14, wherein the curable compound comprises an additional component E, and the additional component E catalyzes the reaction between the at least one crosslinking component A and the at least one second component B. compound. The curable compound according to claim 7, wherein the at least one third component C is a compound having at least two functional groups having an epoxy function. The method of claim 7, wherein the mixing ratio between the component A, the component B and the component C is the component A, the component B after the occurrence of the first and second events in the at least one first region (i). And at least 99% of the component C is incorporated into at least one of the crosslinking systems formed, and 1% or less of the functional groups of the component A, the component B, and the component C remain, and the at least one second region In (ii) at least 99% of the component A, the component B and the component C are incorporated into the second crosslinking system 7 after the sole occurrence of the second event and the component A, the component B and the component C A curable compound, characterized in that it is selected so that 1% or less of the functional groups remain. The curable compound according to claim 7, wherein the curable compound contains at least one filler or reinforcing material in an amount of 1 to 99% by weight. delete delete

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